Chemical compositions, sensory and antioxidative properties of salted shrimp paste (Ka-pi) in Thailand

International Food Research Journal 22(4): 1454-1465 (2015)
Journal homepage: http://www.ifrj.upm.edu.my

Chemical compositions, sensory and antioxidative properties of salted
shrimp paste (Ka-pi) in Thailand
1

Pongsetkul, J., 1,*Benjakul, S., 1Sampavapol, P., 2Osako, K. and 1Faithong, N.

1

Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai,
Songkhla, 90112, Thailand
2
Department of Food Science and Technology, Tokyo University of Marine Science and
Technology, 5-7 Konan 4, Minato-ku, Tokyo, 108-8477, Japan

Article history

Abstract

Received: 16 August 2014
Received in revised form:
5 January 2015
Accepted: 13 January 2015

Chemical compositions, sensory and antioxidative properties of 11 salted shrimp paste (Ka-pi)
obtained from various places of Thailand were determined. Different salted shrimp pastes had
varying amino acid compositions. Glu/Gln and Asp/Asn were the major amino acids. Among
all samples, S9 (Kapi Rayong), which had the highest total amino acid (68.95 mg/g sample),
generally had the highest sensory score for all attributes. Volatile compounds varied in types
and abundance among samples, but pyrazine derivatives were the major volatile components
in all samples. Browning intensity and intermediate browning products were different between
samples. The highest antioxidative activities as determined by DPPH, ABTS, H2O2 radical and
singlet oxygen scavenging activities, FRAP and metal chelating activity were found for S1
(Kapi Satun). Therefore, salted shrimp pastes having nutritive value and antioxidative activity
were different in sensory property, thereby determining the consumer acceptability.

Keywords
Salted shrimp paste
Fermented food

Kapi
Antioxidative activities
MRPs

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Introduction
Kapi is a traditional salted shrimp paste of Thailand.
It is mainly produced from the marine shrimp or krill
(Acetes or Mesopodopsis species), which are mixed
with salt at a ratio of 3-5:1. The moisture content is
decreased by sun drying, and then it is thoroughly
blended or homogenized to produce semi-solid
paste. The paste is fermented for two months until
the desired lavor is developed (Phithakpol, 1993).
Kapi is usually used as a condiment to enhance the
palatability of foods (Yoshida, 1998). Kapi is very
rich in umami taste and contains high amounts of
free glutamic acid (647 mg/100 g) (Mizutani et al.,
1987). Salted shrimp paste has slight cheese-like

lavor and an appetite-stimulating aroma (Peralta
et al., 2008). More than 150 volatile compounds
have been identiied in ish and shrimp pastes (Cha
et al., 1998). The compounds consist of aldehydes,
ketones, alcohols, aromatic compounds, N-containing
compounds, esters, S-containing compounds and
some other compounds. Previous studies noted
that the presence of these S-containing compounds
may affect the overall lavor because of their low
thresholds (Maga and Katz, 1979; Agrahar-Murugkar
and Subbulakshmi, 2006). During fermentation, the
transformation of organic substances into simpler
*Corresponding author.
Email: soottawat.b@psu.ac.th
Tel: 66 7428 6334; Fax: 66 7455 8866

compounds such as peptides, amino acids, and
other nitrogenous compounds either by the action of
microorganisms or endogenous enzymes takes place.
Peptides and amino acids are important contributors

to the lavor and aroma of fermented products
(Raksakulthai and Haard, 1992). Furthermore, the
fermented ish products containing active peptides or
free amino acids generated throughout fermentation
from both endogenous and exogenous enzymes
(Rajapakse et al., 2005). Recently, some fermented
shrimp and krill products have been reported to
exhibit strong antioxidant activities (Faithong et al.,
2010). However, a little information regarding amino
acid compositions, volatile compounds, antioxidative
activities and sensory properties of salted shrimp
paste (Kapi) produced in Thailand has been reported.
Thus, the objective of this study was to determine
chemical composition, sensory and antioxidative
properties of salted shrimp pastes collected from
various regions of Thailand.
Materials and Methods
Chemicals
All chemicals were of analytical grade.
2,4,6-trinitrobenzene-sulphonic

acid
(TNBS),
2,20-azinobis(3-ethylbenzothiazoline-6-sulphonic

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acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH),
2,4,6-tripyridyltriazine
(TPTZ),
3-(2-pyridyl)5,6-diphenyl-1,2,4-triazine-4’,4’’-disulphonic
acid
sodium salt (ferrozine), ethylenediaminetetraacetic
acid
(EDTA),
hydrogen
peroxide
(H2O2),
5,5-dimethyl-1-pyrroline N-oxide (DMPO), N,Ndimethyl ρ-nitrosoaniline (DPN), histidine, sodium

hypochlorite (NaOCl) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were
purchased from Sigma Chemical Co. (St. Louis, MO,
USA).

Collection and preparation of samples
Salted shrimp paste samples were purchased
from different provinces in Thailand, including
Songkhla (2 samples), Ranong (2 samples), Krabi (2
samples), Satun (1 sample), Samut Sakorn (1 sample),
Rayong (1 sample), Chachoengsao (1 sample) and
Samut Songkram (1 sample). Each sample was
separated into several portions (100 g each), placed
in polyethylene bag and heat-sealed. The samples
were kept at -20°C and the storage time was not
longer than 2 months. All samples were subjected to
analyses.
Determination of amino acid compositions
Amino acid compositions of salted shrimp pastes
were determined according to the method of Minh
Tauy et al. (2014) with a slight modiication. Twenty

milligrams of sample were hydrolyzed in 6 M HCl at
110°C for 22 h under vacuum. The hydrolysate was
neutralized with 6 M and 0.6 M NaOH, and iltered
through a cellulose membrane ilter (0.45 µm; Toyo
Roshi Kaisha, Ltd., Tokyo, Japan). The iltrate was
used for amino acid analysis using an amino acid
analysis system (Prominence; Shimadzu, Kyoto,
Japan) equipped with a column (Shim-pack AminoLi, 100 mm × 6.0 mm i.d.; column temperature,
39.0°C; Shimadzu) and pre-column (Shim-pack ISC30/S0504 Li, 150 mm × 4.0 mm i.d.; Shimadzu).
Amino acids were detected using a luorescence
detector (RF-10AXL; Shimadzu, Kyoto, Japan).
Determination of volatile compounds
The volatile compounds of different salted
shrimp pastes were determined using a solidphase microextraction gas chromatography mass
spectrometry (SPME GC-MS) following the
method of Iglesias and Medina (2008) with a slight
modiication.
Extraction of volatile compounds by SPME iber
To extract volatile compounds, 5 g of salted
shrimp paste was mixed with 10 ml of deionized

water. The mixture was homogenized at a speed
of 13,000×g for 1 min to disperse the sample. The
homogenate was placed in a 20-ml headspace vial
(Supelco, Bellefonte, PA, USA) for each SPME.
The vials were tightly capped with a PTFE septum
and heated at 60°C with equilibrium time of 10 h.
The SPME iber (50/30 lm DVB/Carboxen™/PDMS
StableFlex™) (Supelco, Bellefonte, PA, USA) was
conditioned at 270ºC for 15 min before use and then
exposed to the headspace. The 20 ml-vials (Agilent
Technologies, Palo Alto, CA, USA) containing the
sample extract and the volatile compounds were
allowed to absorb into the SPME iber at 60ºC for 1
h. The volatile compounds were then desorbed in the
GC injector port for 15 min at 270ºC.
GC-MS analysis
GC-MS analysis was performed in a HP 5890
series II gas chromatography (GC) coupled with HP
5972 mass-selective detector equipped with a splitless

injector and coupled with a quadrupole mass detector
(Hewlett Packard, Atlanta, GA, USA). Compounds
were separated on a HP-Innowax capillary column
(Hewlett Packard, Atlanta, GA, USA) (30 m ± 0.25
mm ID, with ilm thickness of 0.25 µm). The GC oven
temperature program was: 35ºC for 3 min, followed
by an increase of 3ºC/min to 70ºC, then an increase of
10ºC/min to 200ºC, and inally an increase of 15ºC/
min to a inal temperature of 250ºC and holding for
10 min. Helium was employed as a carrier gas, with a
constant low of 1 ml/min. The injector was operated
in the splitless mode and its temperature was set at
270ºC. Transfer line temperature was maintained
at 260ºC. The quadrupole mass spectrometer was
operated in the electron ionization (EI) mode and
source temperature was set at 250ºC. Initially,
full-scan-mode data was acquired to determine
appropriate masses for the later acquisition in scan
mode under the following conditions: mass range:
25-500 amu and scan rate: 0.220 s/scan. All analyses

were performed with ionization energy of 70 eV,
ilament emission current at 150 µA, and the electron
multiplier voltage at 500 V.
Analyses of volatile compounds
Identiication of the compounds was done by
consulting ChemStation Library Search (Wiley
275.L). Quantitative determination was carried out
using an internal calibration curve that was built
using stock solutions of the compounds in ultra-pure
water saturated in salt and analyzing them by the
optimized HS-SPME method. Quantiication limits
were calculated to a signal-to-noise (S/N) ratio of 10.
Repeatability was evaluated by analyzing 3 replicates

Pongsetkul et al./IFRJ 22(4): 1454-1465

1456

of each sample. The identiied volatile compounds
were presented in the term of abundance.

water and the absorbance was measured at 420 nm
using UV-1601 spectrophotometer.

Sensory properties
Samples were evaluated by 30 untrained
panelists, who consume salted shrimp paste regularly.
The samples were cut to obtain a thickness of 1 cm.
The sample (2×2 cm2) was wrapped with aluminum
foil and heated in hot air oven at 60°C for 30 min.
The samples were served in white paper plate at
room temperature. All samples was coded with three
digit random numbers and divided into 3 groups
(4, 4 and 3 samples). Each group was randomly
served. The panelists were allowed to rest for at
least 15 min between different groups. Panelists
were instructed to rinse their mouths with water or
cucumber between different samples. Evaluations
were made in individual sensory evaluation booths
under luorescent white light. The panelists were
asked to assess samples for appearance liking, color
liking, odor liking, lavor liking, texture liking and
overall liking using a 9-point hedonic scale (1 =
dislike extremely, 9 = like extremely) (Mellgard et
al., 2007).

Measurement of luorescence intensity
Fluorescent
intermediate
products
from
Maillard reaction in the extract were determined as
described by Morales and Jimenez-Perez (2001).
The luorescence intensity of appropriately diluted
extract was measured at an excitation wavelength of
347 nm and emission wavelength of 415 nm using a
luorescence spectrophotometer RF-1501 (Shimadzu,
Kyoto, Japan).

Browning and Maillard reaction product
Preparation of water extract
The extract was prepared according to the method
of Peralta et al. (2008) with a slight modiication.
The salted shrimp paste (2 g) was mixed with 50 ml
of distilled water. The mixtures were homogenized
using an IKA Labortechnik homogenizer (Selangor,
Malaysia) at a speed of 10,000×g for 2 min. The
homogenates were then subjected to centrifugation
at 13,000×g for 15 min at room temperature (Model
RC-B Plus centrifuge Newtown, CT, USA). The
supernatant was collected. The pellet was re-extracted
as described above. The supernatants were combined
and adjusted to 50 ml using distilled water.
Measurement of absorbance at 280 and 295 nm
A280 and A295 of the extract were determined
according to the method of Ajandouz et al. (2001).
The absorbance of the appropriately diluted extract
was measured at 280 and 295 nm using UV-1601
spectrophotometer (Shimadzu, Kyoto, Japan)
to monitor the formation of Maillard reaction
intermediate products.
Measurement of browning intensity
The browning intensity of the extract was
measured according to the method of Benjakul et al.
(2005). Appropriate dilution was made using distilled

Antioxidative properties
Water extract from different salted shrimp pastes
were subjected to determination of antioxidative
activity using various assays.
DPPH radical scavenging activity
DPPH radical scavenging activity was
determined according to the method of Wu et al.
(2003) with a slight modiication. The extract (1.5
ml) was added with 1.5 ml of 0.15 mM 2,2-diphenyl1-picrylhydrazyl (DPPH) in 95% ethanol. The
mixture was then mixed vigorously and allowed to
stand for 30 min in dark at room temperature. The
resulting solution was measured at 517 nm using an
UV-1601 spectrophotometer. The blank was prepared
in the same manner except that distilled water was
used instead of the sample. The standard curve was
prepared using Trolox in the range of 10-60 µM. The
activity was expressed as µmol Trolox equivalents
(TE)/g sample.
ABTS radical scavenging activity
ABTS radical scavenging activity was determined
as described by Amao et al. (2001) with a slight
modiication. The stock solutions included 7.4 mM
ABTS solution and 2.6 mM potassium persulfate
solution. The working solution was prepared by
mixing two stock solutions in equal quantities and
allowed them to react in the dark for 12 h at room
temperature. The solution was then diluted by mixing
1 ml of ABTS solution with 50 ml of methanol to
obtain an absorbance of 1.1 (±0.02) at 734 nm using
an UV-1601 spectrophotometer. ABTS solution
was prepared freshly for each assay. To initiate the
reaction, 150 µl of sample was mixed with 2.85 ml of
ABTS•+ solution. The mixture was incubated at room
temperature for 2 h in dark. The absorbance was then
read at 734 nm using an UV-1601 spectrophotometer.
A Trolox standard curve (50-600 µM) was prepared.
Distilled water was used instead of the sample and
prepared in the same manner to obtain the control.

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ABTS radical scavenging activity was expressed as
µmol Trolox equivalents (TE)/g sample.
Ferric reducing antioxidant power (FRAP)
FRAP was evaluated by the method of Benzie
and Strain (1996). The stock solutions included 10
mM TPTZ (2,4,6-tripyridyl-s-triazine) solution in 40
mM HCl, 20 mM FeCl3.6H2O solution and 300 mM
acetate buffer (pH 3.6). The working solution was
prepared freshly by mixing 25 ml of acetate buffer,
2.5 ml of TPTZ solution and 2.5 ml of FeCl3.6H2O
solution. The mixture was incubated at 37°C for 30
min and was referred to as FRAP solution. The sample
(150 µl) was mixed with 2.85 ml of FRAP solution.
The mixture was allowed to stand in dark for 30
min at room temperature. Ferrous tripyridyltraizine
complex, colored product, was measured by reading
the absorbance at 593 nm. The standard curve was
prepared using Trolox ranging from 50 to 600
µM. The activity was expressed as µmol Trolox
equivalents (TE)/g sample.

(DPN), 0.2 ml of 100 mM histidine, 0.2 ml of 100 mM
sodium hypochlorite, and 0.2 ml of 100 mM H2O2.
Thereafter, the total volume was made up to 2 ml
with 45 mM sodium phosphate buffer (pH 7.4). The
absorbance of the reaction mixture was measured at
440 nm after incubation at room temperature (25°C)
for 40 min. Sample blank was run for each sample in
the same manner, except DPN, histidine, and NaOCl
solutions were replaced by sodium phosphate buffer.
A standard curve of Trolox (0-10 mM) was prepared.
Singlet oxygen scavenging activity was expressed as
µmol Trolox equivalents (TE)/g sample.
Statistical analysis
All analyses were conducted in triplicate.
Statistical analysis was performed using one-way
analysis of variance (ANOVA). Mean comparison
was carried out using Duncan’s multiple range test
(Steel et al., 1980). SPSS statistic program (Version
10.0) (SPSS, 1.2, 1998) was used for data analysis.
Results and Discussion

Metal chelating activity
Metal chelating activity was investigated as
described by Decker and Welch (1990) with a slight
modiication. Sample (220 µl) was mixed with 5 µl
of 2 mM FeCl2 and 10 µl of 5 mM ferrozine. The
mixture was allowed to stand at room temperature for
20 min. Absorbance at 562 nm was read. EDTA with
the concentrations of 0-30 µM was used as standard.
Metal chelating activity was expressed as µmol
EDTA equivalent (EE)/g sample.
Hydrogen peroxide radical scavenging activity
Hydrogen
peroxide
scavenging
activity
was assayed according to the method of
Kittiphattanabawon et al. (2012). The extract (3.4
ml) was mixed with 600 µl of 43 mM hydrogen
peroxide in 0.1 M phosphate buffer (pH 7.4). The
absorbance at 230 nm of the reaction mixture was
recorded after 40 min of reaction at 25°C. For sample
blank, hydrogen peroxide was omitted and replaced
by 0.1 M phosphate buffer (pH 7.4). Trolox (0-10
mM) was used as standard. The hydrogen peroxide
scavenging activity was expressed as µmol Trolox
equivalents (TE)/g sample.
Singlet oxygen scavenging activity
Singlet oxygen scavenging activity was
determined as described by Kittiphattanabawon et al.
(2012). The chemical solutions and the extract were
prepared in 45 mM sodium phosphate buffer (pH 7.4).
The reaction mixture consisted of 0.4 ml of extract,
0.5 ml of 200 µM N,N-dimethyl para-nitro-soaniline

Amino acid compositions
Amino acid compositions of 11 salted shrimp
pastes are presented in Table 1. Total amino acid
content varied among the samples. S9 (Kapi Rayong)
had the highest total amino acid (68.95 mg/g sample).
Coincidentally, the highest total essential amino acid
content (25.16 mg/g sample) was also found for S9.
In general, Glu/Gln and Asp/Asn were the major
amino acids in salted shrimp paste. Gly, Leu and
Lys were also found at a high extent in all samples.
Xu et al. (2008) reported that ish sauce produced
from squid by-product was rich in Glu, Asp, Cys,
Leu and Ala (12.10, 9.33, 8.44, 7.32 and 7.22 mg/g
sample respectively). The differences in amino acid
compositions among the samples were more likely
due to the difference in fermentation and processes
used. Differences in raw material, especially shrimp
or krill, were also presumed. Amino acids mainly
contributed signiicantly to the taste and odor of
salted shrimp paste. The typical lavor of Glu is
meaty (Xu et al., 2008). Taste of salted shrimp paste
was inluenced by Glu for umami and by Asp for
sweetness (Kim et al., 2005). Gly, Ala, Ser and Thr
are also associated with sweetness (Liu, 1989). The
contribution of amino acids to the aroma of ish sauce
was reported by Lopetcharat et al. (2001). Based on
the result, salted shrimp paste could be an excellent
source of amino acids, particularly essential amino
acids. Additionally, those amino acids more likely
contributed to taste and lavor of salted shrimp paste.

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1458

Table 1. Amino acid composition of different salted shrimp pastes*

*
S1 (Kapi Satun); S2 (Kapi Ranong1); S3 (Kapi Ranong2); S4 (Kapi Krabi1); S5 (Kapi Krabi2); S6 (Kapi Songkhla1); S7
(Kapi Songkhla2); S8 (Kapi Samut Sakorn); S9 (Kapi Rayong); S10 (Kapi Chachoengsao); S11 (Kapi Samut Songkram)
A: Essential amino acid in adults.
B: Essential amino acid in children.
C: Essential amino acid.
D: Non-essential amino acid.

Volatile compounds
Volatile compounds of different salted shrimp
samples produced in Thailand were determined using
a solid-phase microextraction gas chromatography
mass spectrometry (SPME GC-MS). Different
volatile compounds were identiied. Those consisted
of alcohols, aldehydes, ketones, hydrocarbon and
nitrogen-containing compounds.
Nitrogen-containing compounds, especially
pyrazine derivatives, seemed to be the major volatile
components in salted shrimp pastes. 2,5-dimethyl
pyrazine,
2,6-dimethyl
pyrazine,
3-ethyl,
2,5-dimethyl pyrazine and 6-ethyl, 2,3,5-trimethyl
pyrazine were found in all samples. Pyrazines were
reported to contribute to nutty, roasted and toasted
aromas in many foods (Wong and Bernhard, 1988).
Sanceda et al. (1990) found that pyrazines could
be responsible for the burnt and sweet odors of
Vietnamese ish sauce (nouc-mam). Pyrazines were
reported to be formed by Maillard reaction through
strecker degradations from various nitrogen sources
such as amino acids (Jaffres et al., 2011). Slightly
high pH of shrimp paste (pH 7.2-8.4) could favor
the formation of pyrazine (Sanceda et al., 1990). S6
(Kapi Songkhla1) showed the highest abundance in
2,5-dimethyl-pyrazines, whereas S8 (Kapi Samut
Sakorn) exhibited the highest level of 2,6-dimethyl-

pyrazines. S6 (Kapi Songkhla1) had the highest
abundance in 3-ethyl-2,5-dimethyl-pyrazines and
2,3,5-trimethyl-6-ethyl-pyrazine.
2-butanol and 3-methyl-butanol were found
at high abundance in most samples. Michihata et
al. (2002) noted that butanol derivatives might
be formed by microbial fermentation, especially
regulated by lactic acid bacteria. 1-hexanol,
1-penten-3-ol, 1-octen-3-ol and benzeneethanol were
also found in most samples. Those alcohols might
be the degradation products from lipid oxidation.
3-methyl-butanol was dominant in S9 (Kapi Rayong)
and S10 (Kapi Chachoengsao), whereas 2-butanol
was highest in S5 (Kapi Krabi2). Furthermore, other
alcohols varied with samples. 2-ethyl, 1-hexanol was
found only in S1 (Kapi Satun), while 1-octen-3-ol
was dominant in S10 (Kapi Chachoengsao).
Abundance of aldehydes e.g. pentanal, hexanal,
etc. in salted shrimp pastes was quite low. It was noted
that benzaldehyde, with a pleasant almond, nutty and
fruity aroma (Vejaphan et al., 1988) was found in all
samples. Aldehydes were more likely generated from
lipid oxidation during fermentation. Branched short
chain aldehydes or aromatic aldehydes plausibly
resulted from deamination of amino acids (Steinhaus
and Schieberle, 2007). Groot and Bont (1998)
noted that some bacteria had aminotransferase

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Table 2. Volatile compounds of different salted shrimp pastes*

*
S1 (Kapi Satun); S2 (Kapi Ranong1); S3 (Kapi Ranong2); S4 (Kapi Krabi1); S5 (Kapi Krabi2); S6 (Kapi Songkhla1); S7 (Kapi
Songkhla2); S8 (Kapi Samut Sakorn); S9 (Kapi Rayong); S10 (Kapi Chachoengsao); S11 (Kapi Samut Songkram)
ND: non-detectable

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Table 3. Likeness score of different salted shrimp pastes*

*

S1 (Kapi Satun); S2 (Kapi Ranong1); S3 (Kapi Ranong2); S4 (Kapi Krabi1); S5 (Kapi Krabi2); S6 (Kapi Songkhla1); S7 (Kapi
Songkhla2); S8 (Kapi Samut Sakorn); S9 (Kapi Rayong); S10 (Kapi Chachoengsao); S11 (Kapi Samut Songkram)
Values are given as mean ± SD (n = 3).
Score are based on a 9-point hedonic scale (1: Dislike extremely, 5: Neither like nor dislike, 9: Like extremely).
Different lowercase superscripts within the same row indicate the signiicant differences (p